It is known that a silver halide photographic light-sensitive material is subjected to heat-development to form an image, which is described, for example, in "Shashin Kogaku no Kiso," Hi-ginen Shashin-hen, (1982, published by Korona-sha), pages 242 to 255, and in U.S. Pat. No. 4,500,626.
Further, heat-developable light-sensitive materials wherein use is made of silver halides are a conventionally widely practiced photographic means, because they are excellent in photographic properties, such as sensitivity and gradation, in comparison with the electrophotographic technique, the diazo photographic technique, and the like. For the method of obtaining a color image by subjecting to heat-development a silver halide light-sensitive material, many proposals are made, one of which is a color-development system of forming a dye image by the coupling reaction of the oxidized product of a developing agent and a coupler. With respect to the developing agent and the coupler that can be used in this color-development system, for example, a combination of a p-phenylenediamine-series reducing agent with a phenol or with an active methylene coupler is proposed in U.S. Pat. No. 3,531,256, a p-aminophenol-series reducing agent is proposed in U.S. Pat. No. 3,761,270, and a combination of a sulfonamidophenol-series reducing agent with a four-equivalent coupler is proposed in U.S. Pat. No. 4,021,240.
This method is, however, accompanied by such defects as that color formation at the undeveloped part of undeveloped silver halides remaining after the processing occurs at the time of printing out or with the lapse of time, and that color contamination occurs due to the simultaneous presence of reduced silver and a dye image at the exposed part. To solve these defects, a dye transfer system is proposed, wherein a diffusion dye is formed by heat development and is transferred to an image-receiving layer.
In such a diffusion transfer-type heat-developable light-sensitive material, there are a case wherein an image-receiving layer capable of receiving a dye is formed on the base of the light-sensitive material, and a case wherein an image-receiving layer is formed on a base different from that of the light-sensitive material.
Particularly when use is made of a heat-developable color light-sensitive material, for the purpose of obtaining a dye image high in color purity, it is desirable to use an image-receiving material having a dye image-receiving layer formed on a separate base, to cause the dye to be diffused and transferred, either simultaneously with the formation of the diffusion dye by the color development, or after the formation of the diffusion dye.
The method wherein a diffusible dye is released or formed imagewise by heat development and the resultant diffusible dye is transferred to a dye-fixing element is proposed. In this method, by changing the type of the dye-providing compound to be used or the type of the silver halide to be used, a negative dye image, as well as a positive dye image, can be obtained. More details are described, for example, in U.S. Pat. No. 4,500,625, U.S. Pat. No. 4,483,914, U.S. Pat. No. 4,503,137, U.S. Pat. No. 4,559,290, JP-A-58-149046 ("JP-A" means unexamined published Japanese patent application), JP-A-60-133449, JP-A-59-218443, JP-A-61-238056, EP-A-220 746 (A2), Kokai-giho No. 87-6199, EP-A-210 660 (A2), and the like. These are accompanied by the problem that the sensitivity of the light-sensitive material is lowered, because a color-formed dye has previously been fixed in a dye- providing substance, and it therefore is preferable to realize a system wherein an originally colorless coupler and a developing agent are reacted, to allow the intended dye to diffuse.
As means of forming an image by the above coupling system, heat-developable light-sensitive materials containing a coupler and a color-developing agent precursor capable of releasing a p-phenylenediamine are disclosed, for example, in JP-B-63-36487 ("JP-B" means examined Japanese patent publication), JP-A-5-224381, and JP-A-6-83005; a combination of a ureidoanilin-series reducing agent with an active methylene-type coupler is disclosed in JP-A-59-111148; a light-sensitive material, wherein use is made of a coupler that has a coupling split-off group with a polymer chain and that can release a diffusion dye by color development, is disclosed in JP-A-58-149047; and a technique wherein a combination of a carbamoylhydrazine-series developing agent with an active methylene-type coupler produces/releases a dye, is disclosed in JP-A-09-152705.
However, the color-developing agents or precursors of color-developing agents used in these documents have such problems that the dye image density after transfer is unsatisfactory, and that the development-processing-time dependency is unpreferably large.
As a means of solving these problems, a technique wherein a hydrophilic reducing agent is used as an auxiliary developing agent in combination with a lipophilic reducing agent, and electrons are moved between them, to increase the rate of development, is known, like a method disclosed in JP-A-1-138556. However, this technique has the problem that the development acceleration effect and raw stock storability of the light-sensitive material (the presence or absence of an influence of storage of the unexposed light-sensitive material on the photographic performance) are difficult to secure at the same time. In this respect, the advent of a technique wherein the development acceleration effect and the raw stock storability are secured at the same time has been desired.